C in 7 days - Passing arguments by address

9

Passing arguments by address

#include <stdio.h>
void swap( int *x, int *y ) {
int t = *x;
*x = *y;
*y = t;
}
main() {
int a = 11, b = 99;
printf( "a=%d, b=%d\n", a, b );
swap( &a, &b );
printf( "a=%d, b=%d\n", a, b );
}

$ gcc -o swap swap.c
$ ./swap
a=11, b=99
a=99, b=11

#include <stdio.h>
#include <stdlib.h>
void circ( const double *r, double *area, double *len ) {
const double PI = 3.14159265358979323846; /* see M_PI in math.h */
*area = PI**r**r;
*len = 2*PI**r;
}
int main( int argc, char *argv[] ) {
double r, a, l;
switch ( argc ) {
case 2:
r = atof( argv[1] );
circ( &r, &a, &l );
printf("%f %f\n", a, l);
break;
default:
printf( "%s radius\n", argv[0] );
exit(1);
}
exit(0);
}

$ gcc -o circ circ.c
$ ./circ
./circ radius
$ ./circ 1
3.141593 6.283185

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